After semiconductor dices are fabricated on a wafer, they will need to go through chip probing or wafer sorting to verify their electrical performance. Usually, the toolings for testing semiconductor wafers are probe cards. A probe card is a tooling which should be manufactured before chip probing or wafer sorting. It is installed on the test head of a tester as an interface between a tester and a wafer under test. Conventionally, a vertical probe card comprises a multi-layer printed circuit board, mostly around 30 to 60 wiring layers, which is complex and costly. The multi-layer printed circuit board is further jointing with an even more costly multi-layer ceramic substrate as a probe head. On the multi-layer ceramic substrate, a plurality of probe needles are formed on an exposed surface for probing the electrode, such as pads or bumps, of semiconductor wafers. The vertical probe card is extremely expensive, and for different IC products, it needs to design the corresponding probe card to meet the special layout of bonding pads of wafer under test. Moreover, the components of a vertical probe card can not be reused.
A conventional probe card employing coaxial cables mainly comprises a substrate. The substrate has a front side and a back side, the front side formed with a large ground plane and a plurality of contact points. Wherein the layout of ground plane is to solder the outer shield of coaxial cables on the plane to provide grounding and shielding effects. The contact points on edges of the front side are for providing electrical connection to a tester. On the front side of the substrate, a plurality of outer connecting points are formed for soldering probe needles. The outer connecting points for soldering probe needles and the contact points on the front side are connecting to each other by means of a plurality of coaxial cables. Each of the coaxial cable is electrically connected individually, and can not be modularized. The circuit layers of the substrate can not be reduced, and can only be used for testing low-density electronic products. Furthermore, the substrate of a conventional probe card is a printed circuit board, which has different thermal coefficient from that of a wafer under test. This arises the problem that the probe card is not able to precisely position and contact the wafer while in electrical contact at certain temperatures.
In U.S. Pat. No. 4,731,577 entitled “COAXIAL PROBE CARD”, a multipoint microwave coaxial probe card is disclosed. A printed circuit board has edge connectors and a mounting ring attached to the surface. The mounting ring has a plurality of via, and each is assembled with a microwave connector. These microwave connectors electrically connect to cantilever needles by coaxial cables. A portion of the cantilever needles are joined to the edge connector by conductive wires allowing both high and low frequency signals to be utilized simultaneously. Furthermore, a shield cover in the form of a flat plate encloses the mounting ring to provide RFI and EMI shielding and allows the coaxial probe card to test the microwave semiconductor wafers. However, this conventional coaxial probe card does not have a probe head, and therefore no cantilever needles can be integrated on it. The individual probe needles are manually installed on the coaxial cables. Furthermore, the coaxial probe card can not have the benefits of modularization to reduce manufacturing cost and lead time.